<form id="searchform" method="get" action="<?php bloginfo('url'); ?>">
    <fieldset>
        <input type="text" value="search" name="s" id="s" size="15" onfocus="if (this.value == 'search') {this.value = '';}" onblur="if (this.value == '') {this.value = 'search';}" /><br />
        <input type="submit" value="Go" id="button" />
    </fieldset>
</form>